The proposal is to use molecular genetic methods with Drosophila to tackle problems of differentiation and patterning at various levels, ranging from the establishment of the anterior-posterior axis of the embryo through to the adult with its complex morphology and intricately connected nervous system. The specific subprojects are: "Localization of Pattern Determinants in the Drosophila Egg", "Patterns of Gene Activation in the Drosophila Embryo", "The Bithorax Complex as a Microgenome", "Genetic Specification of Cellular Identity in the Drosophila Nervous System", and "Specification of Neuronal Shape and Connectivity in Drosophila". These five projects utilize very similar methodology, require similar kinds of materials and equipment, and lend themselves to mutual assistance and strong intellectual interaction. The first proposal aims to search for cDNAs representing RNAs localized to either the anterior (A) or posterior (P) poles of the unfertilized egg, with a view to investigating their roles in establishing embryonic pattern, as well as the molecular mechanisms of RNA localization. The second proposal is a molecular genetic and biochemical approach to dissecting the cis-regulatory region required for the expression of the ftz gene in a pattern of stripes along the A-P embryonic axis. The third is to focus on the cis- regulation of the subset of the 400 kb bithorax complex that controls the development of the second through the ninth abdominal segments. This subset includes the homeodomain-containing infra- abdominal genes and additional regions that are required in cis to insure proper development of the abdomen. The fourth proposal is to use specially designed cloning vectors to identify cDNAs that represent rare mRNAs. Preliminary experiments have shown that very large numbers of distinct clones can be obtained and it is proposed to focus on the roles of the corresponding genes in specifying neuronal cell types. The fifth proposal is a genetic and molecular analysis of a gene involved in the formation of a particular identifiable synapse in Drosophila, and the mechanisms by which the genome affects the specificity of neuronal connections.